1. Field of the Invention
The present invention relates to an improved gear wheel/pawl engagement for a reversible ratcheting tool.
2. Description of the Related Art
U.S. Pat. No. 1,957,462 to Kress issued on May 8, 1934 discloses a ratchet wrench including a ratchet wheel 24 housed in a cylindrical recess 23 in the head 22. A pawl 25 is mounted in a second cylindrical recess 26 in the head 22 for controlling movement of the ratchet wheel 24. The pawl 25 is retained in place by a spring-biased plunger 41. Upon rotation of a thumb-piece 58 connected to the pawl 25, the pawl 25 is movable between two positions and thus provides driving and ratcheting of a socket in opposite directions. The pawl 25 is pivoted through a relatively long distance in the head 22, i.e., the head 22 must be relatively large to allow pivotal movement of the pawl 25. Furthermore, the pawl 25 engages with the teeth of the ratchet wheel 24 by only two teeth, i.e., the wrench is not capable of bearing high torque.
U.S. Pat. No. 4,328,720 to Shiel issued on May 11, 1982 discloses a socket wrench including a drive ring 30, a pawl 50 mounted in a recess 52 in the head 21 of the socket wrench and having two toothed portions 56 and 57, and an external latch handle 53 for controlling position of the pawl 50, thereby optionally causing a desired one of the toothed portions 56 and 57 to engage with a ratcheted outer peripheral portion 48 of the drive ring 30 and thus changing the ratcheting direction. Nevertheless, there are too many components in this socket wrench, and the head 21 is relatively large, as it has to receive the components. Processing and assembly for the components are both troublesome and time-consuming. In addition, transmission between the elements for changing the ratcheting direction is not reliable, as the latch handle 53 does not directly actuate the pawl 50. Furthermore, each toothed portion 56, 57 has only two teeth, i.e., the socket wrench is not capable of bearing high torque.
U.S. Pat. No. 5,626,062 to Colvin issued on May 6, 1997 discloses a ratchet wrench including a drive gear 48 mounted in a head 44 thereof. A reversing pawl 60 is mounted in the head 44 and has teeth 62 for engaging the drive teeth 50 of the drive gear 48 to provide driving and ratcheting of the socket 22 in opposite directions that are reversible by movement of the reversing pawl 60 between two positions under control of a reversing lever 102. The reversing pawl 60 is pivoted through a relatively long distance in the head 44, i.e., the head must be large enough to allow pivotal movement of the reversing pawl 60. Furthermore, the pawl 60 engages with the teeth 50 of the drive gear 48 by only two teeth, i.e., the wrench is not capable of bearing high torque.
U.S. Pat. No. 4,762,033 to Chow issued on Aug. 9, 1988 discloses a ratchet wrench including a drive head 30 with inner ratchet teeth 42. A core assembly 34 is rotatably mounted in the drive head 30 and has a tool-coupling stud 56. Mounted in the core assembly 34 is a pawl 46 that engages with the teeth 42. Upon rotation of a control plate 60, the pawl 46 is movable between two positions and thus provides driving and ratcheting of a socket in opposite directions via transmission of an intercoupling, resilient, spring-like wire 104 that is mounted in the core assembly 34. The pawl 46 engages with the teeth 42 by about five teeth and thus may bear higher torque. Nevertheless, the user must use both hands to switch the ratcheting direction. In addition, there are too many components in this wrench, and the head must be relatively large for receiving the components and allowing movement of the pawl 46. Processing and assembly for these components are both troublesome and time-consuming. Furthermore, the wire 104 tends to malfunction as a result of fatigue and thus fails to provide the required switching direction.
U.S. Pat. No. 4,520,697 to Moetteli issued on Jun. 4, 1985 discloses a ratchet wrench including a holed head 22' having inner ratchet teeth 30'. Mounted in the head 22' is a drive member 32' with a hexagonal drive portion 36'. Also mounted in the head 22' is a pawl 54' having a first set of ratchet teeth 58' and a second set of ratchet teeth 60' for selectively engaging with the teeth 30'. A reverser plate 70' is mounted on top of the drive member 32' and includes two reverser pins 74' for connection with the pawl 54'. The ratcheting action is reversible by merely moving the reverser pins 74'. Nevertheless, there are too many components in this wrench, and the head is large, as it has to receive the components. In addition, processing and assembly are both troublesome and time-consuming. Furthermore, the pawl 54' engages with the teeth 30' by only two teeth, i.e., the wrench is not capable of bearing high torque.
U.S. Pat. No. 3,337,014 to Sandrick issued on Aug. 22, 1967 discloses a ratchet wrench including a head 10 provided with internal periphery ratchet teeth 15. Mounted in the head 10 is a double-ended pawl 26 that is pivotable by a spring pressed plunger 38. Upon rotation of a finger piece 36, the pawl 26 is movable between two positions and thus provides driving and ratcheting of a socket in opposite directions. Nevertheless, there are too many components in this wrench, and the head is large, as it has to receive the components. In addition, processing and assembly are both troublesome and time-consuming. The pawl 26 engages with the teeth 15 by only three teeth, i.e., the wrench is not capable of bearing high torque. Furthermore, the user must use both hands to switch the ratcheting direction.
U.S. Pat. No. 5,144,869 to Chow issued on Sep. 8, 1992 discloses a ratchet wrench including a handle with two box ends each having a ratchet wheel 12 mounted therein. A pawl 20 is engaged with each ratchet wheel 12. A knob 30 is mounted in a middle of the handle and receives a disc 40 that is connected to each pawl 20 by two resilient members 26. When the knob 30 and the disc 40 are rotated, the first toothed section 22 and the second toothed section 23 of each pawl 20 are caused to engage with the associated ratchet wheel 12 via transmission by the resilient members 26, thereby controlling the torque transmission direction of the ratchet wheel 12. Nevertheless, the resilient members 26 tend to malfunction as a result of fatigue. In addition, position of each pawl 20 cannot be precisely controlled. The handle structure is weak, as it must be machined to provide a space for receiving the knob 30, the resilient members 26, and the pawls 20. Furthermore, each pawl 20 engages with the ratchet wheel 12 by only two teeth, i.e., the wrench is not capable of bearing high torque.
FIG. 14 of the drawings illustrates a ratcheting tool including a head 11' having a first compartment 121' for receiving a drive member 20' with a ratchet wheel 21', a second compartment 122' for receiving a pawl 30', and a third compartment 123' for receiving a switch block 40'. The pawl 30' includes teeth 31' formed on a first side thereof for engaging with teeth of the ratchet wheel 21'. The switch block 40' includes a first side having two operative sections 416' for selectively bearing against a second side of the pawl 30'. A second side of the switch block 40' includes two arcuate grooves 414'. A thumb piece 42' includes a stem 421' that extends through a hole 13' in the head 11', a vertical hole 413' in the switch block 40', and a hole 71' of a cover 70'. A spring 61' is mounted in a cavity 14' in the web area of the tool for urging a ball 62' to engage with one of the grooves 414'. An elastic ring 50' is wound around a stub 411' on the switch block 40' and includes an engaging end 51' engaged in a hole 32' of the pawl 30'. Upon rotation of the thumb piece 42', the pawl 30' is movable between two positions and thus provides driving and ratcheting of a socket in opposite directions via transmission of the switch block 40' and the elastic ring 50'. The pawl 30' engages with the ratchet wheel teeth by more teeth and thus may bear higher torque. Nevertheless, the pawl 30' has a long travel in the head 11', and the head 11' must be relatively large for receiving the ratchet wheel 21', the pawl 30', and the switch block 40' and allowing pivotal movement of the pawl 30' and the switch block 40'. In addition, the elastic ring 50' is required for transmitting the force from the switch block 40' to the pawl 30' so as to change the ratcheting direction. More specifically, position of the pawl 30' cannot be precisely controlled. In addition, the elastic ring 50' tends to malfunction as a result of fatigue.
In conclusion, the above-mentioned conventional ratcheting tools fail to provide high torque operation, as most of the pawls merely engage with the ratchet wheel by at best three or five teeth. The head of the ratcheting tool has to be relatively large for accommodating those components and thus is difficult to be used in a limited space. Generally, a skilled user uses a combination wrench, a spanner with two open ends, or a ring spanner for tightening or loosening a fastener in a limited space. Yet, it is found that free rotation of the ratcheting tool during ratcheting is too large (larger than the theoretic value of 5.degree.), as the pawl has a long travel.
The present invention is intended to provide an improved gear wheel/pawl engagement for a reversible ratcheting tool that mitigates and/or obviates the above problems.